US biotechnology company Human Genome Sciences (HGS) has adopted a stockholder rights plan, or poison pill, after rejecting GlaxoSmithKline's (GSK's) bid to take over the company for $2.6bn.
The rights plan, which has a term of one year, will be triggered after a person or group commences a tender offer to purchase 15% or more of HGS common stock without prior board approval.
HGS said in a statement that the rights plan will not prevent any offers or transactions that the board determines to be in the best interest of the company and its shareholders.
GSK attempted to acquire all outstanding shares of HGS for $13 a share in cash in April 2012, representing a premium of 81% to HGS's closing share price of $7.17 on 18 April.
The biotech firm said at the time that the offer "does not reflect the value inherent of the company."
Following HGS's rejection, GSK pledged to continue to proceed with its tender offer, which will close on 7 June 2012.